Silicone porous body and method of producing the same

ABSTRACT

The present invention provides, for example, a silicone porous body having a porous structure with less cracks and a high proportion of void space as well as having a strength. The silicone porous body of the present invention includes silicon compound microporous particles, wherein the silicon compound microporous particles are chemically bonded by catalysis. For example, the abrasion resistance measured with BEMCOT® is in the range from 60% to 100%, and the folding endurance measured by the MIT test is 100 times or more. The silicone porous body can be produced, for example, by forming the precursor of the silicone porous body using sol containing pulverized products of a gelled silicon compound and then chemically bonding the pulverized products contained in the precursor of the silicone porous body. The chemical bond among the pulverized products is preferably a chemical crosslinking bond among the pulverized products, for example.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.15/539,926, filed on Jun. 26, 2017, which is a 371 of InternationalApplication No. PCT/JP2015/086362, filed on Dec. 25, 2015, which isbased upon and claims the benefit of priority from the prior JapanesePatent Application No. 2014-266782, filed on Dec. 26, 2014, JapanesePatent Application No. 2015-152967 filed on Jul. 31, 2015, JapanesePatent Application No. 2015-176204 filed on Sep. 7, 2015, the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a silicone porous body and a method ofproducing the same.

BACKGROUND ART

There are lots of examples of a porous structure made by using variousmaterials and production methods. The porous structure is used forproducts in a wide range of fields including optical elements such aslow refractive index layers, heat insulating materials, sound absorbingmaterials, and regenerative medical bases. The porous structure includesa closed-cell structure in which independent void spaces (pores) aredispersed, an open-cell structure in which the closed-cell structuresare interconnected, and the like, which are defined according to thedispersion state of pores. The porous structure can be defined alsoaccording to a size of the void space and various other matters.

As a method of producing such a porous structure, for example, there isa method of substituting a solvent contained in a wet gel with gas underits supercritical condition to obtain a dry gel with no shrinkage inwhich the skeletal structure of the wet gel is frozen as it is (see, forexample, Patent Document 1). This dry gel can be divided into: a xerogelobtained by gradually removing a gel solvent by evaporation under anormal pressure; and an aerogel, which is “a gel like air”, having a lowbulk density and a high porosity.

A common problem in producing an aerogel bulk body is to prevent a gelbody from cracking in drying of the gel. The crack is made when thetensile stress by the capillary force based on the surface tension of asolution remaining in a pore of the gel body in drying is greater thanthe strength of the gel. Under a supercritical condition, a bulk bodywith no crack can be obtained because of no surface tension, however,there is a case that a crack is made during high temperature sinteringtreatment as a process of removing big pores afterwards. For the purposeof reducing cracks to be caused during such high temperature treatment,there are examples of using a solvent having a higher boiling point thanwater and having a small surface tension, mixing silica fine particlesinto a solvent, and the like (Non-Patent Document 1).

On the other hand, forming a silicone porous body having a highproportion of void space (porosity) has a problem that its strengthsignificantly decreases because of decrease in the bulk density of asilica gel material. The decrease in the strength causes a problem inuse, such as decrease in an abrasion resistance. Regarding this matter,there have been disclosed the methods of baking a silicone porous bodyto increase the strength (see, for example, Patent Documents 2 to 5).These methods, however, are premised on a batch process since hightemperature treatment at 200° C. or more is performed for a long periodof time in baking treatment. Thus, a continuous production cannot beperformed industrially. Moreover, the baking treatment has a problem ofcausing cracks because of the great change in volume in cooling uponcompletion of the sintering after the crystal stable phase of a silicagel has been transited from a low-temperature phase to ahigh-temperature phase.

On the other hand, there has also been disclosed a method of applyingalkali treatment to a silica aerogel film to cause a condensationreaction of an unreacted silanol group, thereby increasing the strengthof the silica aerogel film (see, for example, Patent Document 6). Inthis case, however, since a formed silica aerogel film is immersed in analkali treatment solution, a dehydration condensation reaction of theunreacted silanol group due to penetration of the alkaline solution intovoids is assumed to be caused. This causes a silica aerogel film to beswollen and dried, and this decreases the proportion of void space ofthe silica aerogel film after the alkali treatment. The strength and theproportion of void space have a trade-off relationship and it isdifficult to achieve both properties.

CITATION LIST Patent Document (s)

-   Patent Document 1: JP 2005-154195 A-   Patent Document 2: JP 2006-297329 A-   Patent Document 3: JP 2006-221144 A-   Patent Document 4: JP 2006-011175 A-   Patent Document 5: JP 2008-040171 A-   Patent Document 6: JP 2009-258711 A

Non-Patent Document(s)

-   Non-Patent Document 1: T. Adachi, J. Mater. Sci., 22. 4407-4410    (1987)

BRIEF SUMMARY OF THE INVENTION Problem to be Solved by the Invention

Hence, the present invention is intended to provide, for example, asilicone porous body having a porous structure with less cracks and ahigh proportion of void space having a strength, and a method ofproducing the same.

Means for Solving Problem

In order to achieve the above object, the present invention provides asilicone porous body including: silicon compound microporous particles,wherein the silicon compound microporous particles are chemically bondedby catalysis.

The present invention also provides a method of producing a siliconeporous body, including steps of: preparing a liquid containing siliconcompound microporous particles; adding a catalyst for chemically bondingthe silicon compound microporous particles to the liquid; and chemicallybonding the microporous particles by catalysis.

Effects of the Invention

The silicone porous body of the present invention uses the siliconcompound microporous particles and the porous structure is immobilizedby the chemical bond among the silicon compound microporous particles bycatalysis. This allows the present invention to provide a siliconeporous body having a porous structure with less cracks and a highproportion of void space as well as having a strength.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a process cross sectional view schematically showing anexample of the method of forming a silicone porous body 20 on a base 10in the present invention.

FIG. 2 is an illustration schematically showing an example of a part ofthe process of producing a silicone porous body of the present inventionand an example of the apparatus used therefore.

FIG. 3 is an illustration schematically showing another example of apart of the process of producing a silicone porous body of the presentinvention and another example of the apparatus used therefore.

FIG. 4 is a cross sectional SEM image of a silicone porous body of theExample.

FIG. 5 is a TEM image of a microporous particle in a silicone porousbody of the Example.

FIG. 6 is a process cross sectional view schematically showing anotherexample of the method of forming a silicone porous body on a base in thepresent invention.

FIG. 7 is an illustration schematically showing still another example ofa part of the process of producing a silicone porous body of the presentinvention and still another example of the apparatus used therefore.

FIG. 8 is an illustration schematically showing still another example ofa part of the process of producing a silicone porous body of the presentinvention and still another example of the apparatus used therefore.

FIG. 9 is a process cross sectional view showing still another exampleof the method of forming a silicone porous body on a base in the presentinvention.

FIG. 10 is an illustration schematically showing still another exampleof a part of the process of producing a silicone porous body of thepresent invention and still another example of the apparatus usedtherefore.

FIG. 11 is an illustration schematically showing still another exampleof a part of the process of producing a silicone porous body of thepresent invention and still another example of the apparatus usedtherefore.

DETAILED DESCRIPTION OF THE INVENTION

The porous structure of the silicone porous body of the presentinvention is an open-cell structure in which pore structures areinterconnected, for example.

In the production method of the present invention, for example, thecatalyst promotes the crosslinking bond among silicon compound sols.

The present invention is described below in more detail with referenceto illustrative examples. The present invention, however, is not limitedor restricted by the following description.

[1. Silicone Porous Body]

As described above, the silicone porous body of the present invention ischaracterized in that it includes silicon compound microporousparticles, wherein the silicon compound microporous particles arechemically bonded by catalysis. In the present invention, the shape ofthe “particle” (for example, the silicon compound microporous particle)is not limited to particular shapes, and can be, for example, aspherical shape, a non-spherical shape, and the like.

The silicone porous body of the present invention has athree-dimensional structure by chemical bond (for example, crosslinking)among the silicon compound microporous particles by catalysis. Thesilicone porous body of the present invention having such aconfiguration, despite its structure with void spaces, can maintain asufficient strength and sufficient flexibility for reducing cracks.Thus, the silicone porous body of the present invention can be used forvarious members as a bulk body or a film having a porous structure, forexample. Specifically, the silicone porous body of the present inventioncan be used, for example, as optical elements such as low refractiveindex layers, heat insulating materials, sound absorbing materials,regenerative medical bases, dew condensation preventing materials, andink image receiving members. The silicone porous body of the presentinvention is particularly preferably a xerogel, for example, although itdiffers depending on applications and purposes. Heretofore, the xerogelhas been superior in strength but inferior in proportion of void space,whereas the aerogel has been high in proportion of void space but low instrength. In this regard, the silicone porous body of the presentinvention achieves both a high proportion of void space and a highstrength. In other words, the silicone porous body of the presentinvention achieves a high proportion of void space as in the case of anaerogel even with a xerogel, for example. Furthermore, in the siliconeporous body of the present invention, the silicon compound microporousparticle is preferably a pulverized product of a gelled siliconcompound. The pulverized products of a gelled silicon compound form anew three-dimensional structure which is different from the structureformed of unpulverized gelled silicon compounds, and a chemical bond(for example, crosslinking) is formed among the pulverized products.This allows the silicone porous body of the present invention to achieveproperties (for example, sufficient strength, sufficient flexibility,and the like), which are different from those of a porous body formed ofunpulverized gelled silicon compounds. In the present invention, thesilicon compound microporous particle may be, for example, a sol-gelbeaded particle, a nanoparticle (hollow nanosilica/nanoballoonparticle), nanofiber, and the like.

As described above, the silicone porous body of the present inventionincludes the silicon compound microporous particles (preferably,pulverized products of a gelled silicon compound), wherein the siliconcompound microporous particles are chemically bonded by catalysis. Inthe silicone porous body of the present invention, the pattern of thechemical bond among the silicon compound microporous particles is notlimited to particular patterns. Specifically, the chemical bond can be,for example, a crosslinking bond. The method of chemically bonding thesilicon compound microporous particles is described in detail in thedescription as to the production method of the present invention.

The crosslinking bond is, for example, a siloxane bond. The chemicalbond of the present invention, however, is not limited to a siloxanestructure. Examples of the siloxane bond include T2 bond, T3 bond, andT4 bond shown below. In the case where the silicone porous body of thepresent invention has the siloxane bond, the porous body of the presentinvention may have one of, two of, or all of the above-mentioned threebond patterns, for example. The silicone porous body having higherproportions of T2 and T3 is superior in flexibility and can be expectedto have an original property of a gel but is inferior in strength. Onthe other hand, the silicone porous body having a higher proportion ofT4 is superior in strength but has small sized voids and is inferior inflexibility. Thus, it is preferable to change the proportions of T2, T3,and T4 depending on applications, for example.

In the case where the silicone porous body of the present invention hasthe siloxane bond, the relative ratio among T2, T3, and T4 with T2 beingconsidered as “1” is, for example, as follows:

T2:T3:T4=1: [1 to 100]:[0 to 50], 1:[1 to 80]:[0 to 40], or 1:[5 to60]:[0 to 30].

The silicon atoms contained in the silicone porous body of the presentinvention are preferably bonded by a siloxane bond, for example. As aspecific example, the proportion of the unbonded silicon atoms (i.e.,residual silanol) among all the silicon atoms contained in the siliconeporous body is, for example, less than 50%, 30% or less, or 15% or less.

The silicon compound microporous particle is not limited to particularparticles, and is preferably a pulverized product of a gelled siliconcompound as described above. The gel form of the gelled silicon compoundis not limited to particular forms. The “gel” commonly denotes asolidified state of solutes aggregated as they lost independent motilitydue to interaction. Commonly, a wet gel is a gel containing a dispersionmedium in which solutes build a uniform structure, and a xerogel is agel from which a solvent is removed and in which solutes form a networkstructure with void spaces. In the present invention, the gelled siliconcompound is preferably a wet gel, for example.

The silicone porous body of the present invention has a pore structure,for example. The size of a void space (pore) in the present inventionindicates not the diameter of the short axis but the diameter of thelong axis of the void space. The size of a void space (pore) ispreferably in the range from 5 nm to 10 cm, for example. The lower limitof the size of a void space is, for example, 5 nm or more, 10 nm ormore, or 20 nm or more, the upper limit of the size of a void space is,for example, 10 cm or less, 1 mm or less, or 1 μm or less, and the sizeof a void space is, for example, in the range from 5 nm to 10 cm, 10 nmto 1 mm, or 20 nm to 1 μm. A preferable size of a void space changesdepending on applications of the void-provided structure. Thus, the sizeof a void space should be adjusted to a desired size according topurposes, for example. A preferable example of the pore structure in thesilicone porous body of the present invention is, for example, as shownin FIG. 4 (cross sectional SEM image) in the Examples below. FIG. 4however is an example and does not limit the present invention by anymeans. The size of a void space can be evaluated, for example, by themethod described below.

(Observation of Cross Section of Silicone Porous Body Using SEM)

In the present invention, the form of a silicone porous body can beobserved and analyzed using a scanning electron microscope (SEM).Specifically, for example, a silanol porous body sample formed on aresin film is subjected to a FIB processing (acceleration voltage: 30kV) under a cooling condition, the thus obtained cross sectional sampleis observed using FIB-SEM (product of FEI, product name: Helios NanoLab600, acceleration voltage: 1 kV), and a cross sectional electron imagecan be obtained with an observation magnification×100,000.

(Evaluation of Size of Void Space)

In the present invention, the size of a void space can be quantifiedaccording to the BET test. Specifically, 0.1 g of a sample (the siliconeporous body of the present invention) is set in the capillary of asurface area measurement apparatus (product of Micrometrics, productname: ASAP 2020), and dried under a reduced pressure at room temperaturefor 24 hours to remove gas in the void-provided structure. Then, anadsorption isotherm is created by adsorbing a nitrogen gas to thesample, thereby obtaining a pore distribution. The size of a void spacecan thereby be evaluated.

The abrasion resistance of the silicone porous body of the presentinvention measured with BEMCOT® is, for example, in the range from 60%to 100%. The abrasion resistance means, for example, a strength such asa film strength. The present invention having such a strength has asuperior abrasion resistance in various processes, for example. Thepresent invention has a scratch resistance during a production processincluding winding a formed silicone porous body and handling a productfilm, for example. The silicone porous body of the present invention canincrease a film strength while adjusting a film density, for example.Specifically, by utilizing the catalysis in the heating step describedbelow, the bonding force among the silicon compound microporousparticles can be increased by subjecting silanol groups of the siliconcompound microporous particles (preferably, silica sol fine particles;more preferably, silica sol fine particles obtained by pulverizing agelled silica compound) to a crosslinking reaction. By adjusting thebalance between the amount of the residual silanol group and thecrosslinking reaction, a film strength can be imparted while controllinga porosity. Thus, the silicone porous body of the present invention canimpart a certain level of strength to a void-provided structure which isintrinsically fragile, for example.

The lower limit of the abrasion resistance is, for example, 60% or more,80% or more, or 90% or more, and the upper limit of the abrasionresistance is, for example, 100% or less, 99% or less, or 98% or less,and the abrasion resistance is, for example, in the range from 60% to100%, 80% to 99%, or 90% to 98%.

The abrasion resistance can be measured, for example, by the methoddescribed below.

(Evaluation of Abrasion Resistance)

(1) A layer with void spaces (the silicone porous body of the presentinvention, herein after also referred to as a “void-provided layer”)formed on an acrylic film by coating is cut into a circle having adiameter of about 15 mm as a sample.(2) Next, as to the sample, the coating amount of Si (Si₀) is measuredby identifying silicon by X-ray fluorescence (product of ShimadzuCorporation, product name: ZSX Primus II). Subsequently, thevoid-provided layer on the acrylic film in proximity to the site wherethe circular sample was obtained is cut so as to have a piece having asize of 50 mm×100 mm, the obtained piece is fixed to a glass plate(thickness: 3 mm), and a sliding test is performed using BEMCOT®. Thesliding condition is as follows: weight: 100 g, reciprocation: 10 times.(3) The sampling and X-ray fluorescence measurement of the void-providedlayer after finishing sliding are performed in the same manner as theabove described item (1) to measure the residual amount of Si (Si₁)after an abrasion test. The abrasion resistance is defined by theresidual ratio of Si (%) before and after the sliding test usingBEMCOT®, and is represented by the following formula.

abrasion resistance (%)=[residual amount of Si (Si₁)/Si coating amount(Si₀)]×100(%)

The folding endurance of the silicone porous body of the presentinvention by the MIT test is, for example, 100 times or more. Thefolding endurance shows flexibility, for example. The flexibility meansdeformability of a substance, for example. Since the present inventionhas such flexibility, for example, cracks can be reduced and a superiorwinding ability in production and a superior handleability in use can beachieved, for example.

The lower limit of the folding endurance is, for example, 100 times ormore, 500 times or more, or 1000 times or more, the upper limit of thefolding endurance is not limited to particular values and is, forexample, 10000 times or less, and the folding endurance is, for example,in the range from 100 to 10000 times, 500 to 10000 times, or 1000 to10000 times.

The folding endurance by the MIT test can be measured, for example, bythe method described below.

(Evaluation of Folding Endurance Test)

The void-provided layer (the silicone porous body of the presentinvention) is cut into a piece having a size of 20 mm×80 mm, then theobtained piece is attached to a MIT folding endurance tester (productionof TESTER SANGYO CO., LTD., product name: BE-202), and 1.0 N load isapplied thereto. A chuck of R 2.0 mm for holding the void-provided layeris used, application of load is at most 10000 times, and the number oftimes of application of load at the time of fracture of thevoid-provided layer is assumed as the folding endurance.

The film density of the silicone porous body of the present invention isnot limited to particular values, and the lower limit thereof is, forexample, 1 g/cm³ or more, 10 g/cm³ or more, or 15 g/cm³ or more, theupper limit thereof is, for example, 50 g/cm³ or less, 40 g/cm³ or less,30 g/cm³ or less, or 2.1 g/cm³ or less, and the film density is, forexample, in the range from 5 to 50 g/cm³, 10 to 40 g/cm³, 15 to 30g/cm³, or 1 to 2.1 g/cm³. In the silicone porous body of the presentinvention, the porosity based on the film density is not limited toparticular values, and the lower limit thereof is, for example, 40% ormore, 50% or more, 70% or more, or 85% or more, the upper limit thereofis, for example, 98% or less, or 95% or less, and the porosity is, forexample, in the range from 40% to 98%, 50% to 95%, 70% to 95%, or 85% to95%.

The film density can be measured, for example, by the method describedbelow, and the porosity can be calculated, for example, as follows basedon the film density.

(Evaluation of Film Density and Porosity)

After forming a void-provided layer (the silicone porous body of thepresent invention) on a base (acrylic film), the X-ray reflectivity in atotal reflection region of the void-provided layer of this laminate ismeasured using an X-ray diffractometer (product of RIGAKU, product name:RINT-2000). Then, after fitting with Intensity at 20, the film density(g/cm³) is calculated from the total reflection angle of the laminate(void-provided layer and base), and the porosity (P %) is calculated bythe following formula.

porosity (P %)=45.48×film density (g/cm³)+100(%)

It is only required that the silicone porous body of the presentinvention has a pore structure (porous structure) as described above,and the silicone porous body may have an open-cell structure in whichthe pore structures are interconnected, for example. The open-cellstructure means, for example, that the pore structures arethree-dimensionally interconnected in the silicone porous body, i.e.,void spaces in the pore structures are interconnected. When a porousbody has an open-cell structure, the porosity of the silicone porousbody can be increased. However, an open-cell structure cannot be formedwith closed-cell particles such as hollow silica. In this regard, sincethe silicon compound microporous particles (preferably, silica sol fineparticles; more preferably, silica sol fine particles which arepulverized products of a gelled silicon compound which forms sol) have athree-dimensional dendritic structure, the silicone porous body can forman open-cell structure easily, for example, by settlement and depositionof the dendritic particles in a coating film (sol coating filmcontaining the silica sol fine particles) during a production process.The silicone porous body of the present invention preferably forms amonolith structure in which the open-cell structure has multiple poredistributions. The monolith structure denotes a hierarchical structureincluding a structure in which nano-sized void spaces are present and anopen-cell structure in which the nano-sized spaces are aggregated, forexample. The monolith structure can impart a strength with minute voidspaces while imparting a high porosity with coarse open-cell structure,which achieve both a strength and a high porosity, for example. Forforming such a monolith structure, for example, it is preferable tocontrol the pore distribution of a void-provided structure to be createdin a gel (gelled silicon compound) before pulverizing into the silicasol fine particles. For example, by controlling the particle sizedistribution of silica sol fine particles after pulverization to adesired size in pulverization of the gelled silicon compound, themonolith structure can be formed.

In the silicone porous body of the present invention, the haze showingtransparency is not limited to particular values, and the lower limitthereof is, for example, 0.1% or more, 0.2% or more, or 0.3% or more,the upper limit thereof is, for example, 30% or less, 10% or less, or 3%or less, and the haze is, for example, in the range from 0.1% to 30%,0.2% to 10%, or 0.3% to 3%.

The haze can be measured, for example, by the method described below.

(Evaluation of Haze)

A void-provided layer (the silicone porous body of the presentinvention) is cut into a piece having a size of 50 mm×50 mm, and theobtained piece is set to a hazemeter (product of Murakami Color ResearchLaboratory, product name: HM-150) to measure a haze. The haze value iscalculated by the following formula.

haze (%)=[diffuse transmittance (%)/total light transmittance(%)]×100(%)

Commonly, a ratio between the transmission speed of the wavefront oflight in vacuum and the phase velocity of light in a medium is called arefractive index of the medium. The refractive index of the siliconeporous body of the present invention is not limited to particularvalues, and the upper limit thereof is, for example, 1.25 or less, 1.20or less, or 1.15 or less, the lower limit thereof is, for example, 1.05or more, 1.06 or more, or 1.07 or more, and the refractive index is, forexample, in the range from 1.05 to 1.25, 1.06 to 1.20, or 1.07 to 1.15.

In the present invention, the refractive index is a refractive indexmeasured at a wavelength of 550 nm unless otherwise stated. The methodof measuring a refractive index is not limited to particular methods,and the refractive index can be measured, for example, by the methoddescribed below.

(Evaluation of Refractive Index)

After forming a void-provided layer (the silicone porous body of thepresent invention) on an acrylic film, the obtained laminate is cut intoa piece having a size of 50 mm×50 mm, and the obtained piece is adheredto the front surface of a glass plate (thickness: 3 mm) through apressure-sensitive adhesive layer. The center of the back surface of theglass plate (diameter: about 20 mm) is solidly painted with a blackmagic marker, thereby preparing a sample which allows no reflection atthe back surface of the glass plate. The sample is set to anellipsometer (product of J. A. Woollam Japan, product name: VASE), therefractive index is measured at a wavelength of 500 nm and at anincidence angle of 50° to 80°, and the average value is assumed as arefractive index.

The thickness of the silicone porous body of the present invention isnot limited to particular values, and the lower limit thereof is, forexample, 0.01 μm or more or 0.05 μm or more, the upper limit thereof is,for example, 1 m or less, 1 cm or less, or 100 μm or less, and thethickness is, for example, in the range from 0.05 to 100 μm. When thesilicone porous body is used as a film, the thickness is adjustedaccording to applications and required characteristics. The thickness ispreferably 0.01 μm or more and 10 μm or less, for example, in the casewhere priority is put on transmittance, and the thickness is preferably100 μm or more and 1 m or less, for example, in the case where priorityis put on adiabaticity.

The gelled silicon compound can be, for example, a gelled productobtained by gelating monomer silicon compounds. Specifically, the gelledsilicon compound can be, for example, a gelled product in which themonomer silicon compounds are bonded. As a specific example, the gelledsilicon compound can be a gelled product in which the monomer siliconcompounds are bonded by a hydrogen bond or an intermolecular bond. Thebond can be, for example, a bond by dehydration condensation. The methodof gelation is described below in the description as to the productionmethod of the present invention.

In the present invention, the monomer silicon compound is not limited toparticular compounds. The monomer silicon compound can be, for example,a compound represented by the following chemical formula (1). When thegelled silicon compound is a gelled product in which monomer siliconcompounds are bonded by a hydrogen bond or an intermolecular bond asdescribed above, monomers in the chemical formula (1) can be bonded by ahydrogen bond through their hydroxyl groups, for example.

(R¹_(4-x)SiOH)_(x)  (1)

In the chemical formula (1), for example, X is 2, 3, or 4, and R¹represents a linear or a branched alkyl group. The carbon number of R¹is, for example, 1 to 6, 1 to 4, or 1 to 2. Examples of the linear alkylgroup include a methyl group, an ethyl group, a propyl group, a butylgroup, a pentyl group, and a hexyl group, and examples of the branchedalkyl group include an isopropyl group and an isobutyl group. The X is,for example, 3 or 4.

A specific example of the silicon compound represented by the chemicalformula (1) can be a compound represented by the chemical formula (1′),wherein X is 3. In the chemical formula (1′), R¹ is the same as that inthe chemical formula (1), and is, for example, a methyl group. When R¹represents a methyl group, the silicon compound istris(hydroxy)methylsilane. When X is 3, the silicon compound is, forexample, trifunctional silane having three functional groups.

A specific example of the silicon compound represented by the chemicalformula (1) can be a compound represented by the chemical formula (1′)wherein X is 4. In this case, the silicon compound is, for example,tetrafunctional silane having four functional groups.

The monomer silicon compound may be, for example, a hydrolysate of asilicon compound precursor. The silicon compound precursor is notlimited as long as it can generate the silicon compound by hydrolysis,for example. A specific example of the silicon compound precursor can bea compound represented by the following chemical formula (2).

(R¹_(4-x)SiOR²)_(x)  (2)

In the chemical formula (2), for example, X is 2, 3, or 4, R¹ and R²each represent a linear or branched alkyl group, R¹ and R² may be thesame or different, R¹ may be the same or different in the case where Xis 2, and R² may be the same or different.

X and R¹ are the same as those in the chemical formula (1), for example.Regarding R², for example, reference can be made to the examples of R¹in the chemical formula (1).

A specific example of the silicon compound precursor represented by thechemical formula (2) can be a compound represented by the chemicalformula (2′) wherein X is 3. In the chemical formula (2′), R¹ and R² arethe same as those in the chemical formula (2). When R¹ and R² bothrepresent methyl groups, the silicon compound precursor istrimethoxy(methyl)silane (hereinafter, also referred to as “MTMS”).

The monomer silicon compound is not limited to particular compounds, andcan be selected, for example, according to applications of the siliconeporous body of the present invention. In the silicone porous body of thepresent invention, in the case where priority is put on the lowness ofrefractive index, the monomer silicon compound is preferably thetrifunctional silane because it is superior in the lowness of refractiveindex, and in the case where priority is put on a strength (for example,abrasion resistance), the monomer silicon compound is preferably thetetrafunctional silane because it is superior in an abrasion resistance.On the other hand, in the case where priority is put on flexibility, themonomer silicon compound is preferably the difunctional silane becauseit is superior in flexibility. Regarding the monomer silicon compoundswhich are raw materials of the gelled silicon compound, one of thecompounds may be used alone or two or more of them may be used incombination, for example. As a specific example, the monomer siliconcompound may include only the trifunctional silane, only thetetrafunctional silane, or both of the trifunctional silane and thetetrafunctional silane, and may further include other silicon compounds,for example. When two or more kinds of silicon compounds are used as themonomer silicon compound, the ratio between the compounds is not limitedto particular values and can be determined appropriately.

In the silicone porous body of the present invention, the volume averageparticle size showing particle size variations of the silicon compoundmicroporous particle (preferably, a pulverized product of a gelledsilica compound) is not limited to particular values, and the lowerlimit thereof is, for example, 0.05 μm or more, 0.10 μm or more, or 0.20μm or more, the upper limit thereof is, for example, 2.00 μm or less,1.50 μm or less, or 1.00 μm or less, and the volume average particlesize is, for example, in the range from 0.05 μm to 2.00 μm, 0.10 μm to1.50 μm, or 0.20 μm to 1.00 μm. The particle size distribution can bemeasured, for example, using a particle size distribution analyzer basedon optical centrifugal sedimentation, dynamic light scattering, laserdiffraction, or the like or using an electron microscope such as ascanning electron microscope (SEM) or a transmission electron microscope(TEM). The method of measuring the particle size distribution, however,is not limited thereto. In the present invention, the silicon compoundmicroporous particle may definite or indefinite in shape. Preferably,each silicon compound microporous particle has a single or multiplemicropors. In the present invention, a preferable form of the siliconcompound microporous particle is, for example, as shown in FIG. 5 (TEMimage) in the Examples below. FIG. 5 however is an example and does notlimit the present invention by any means. In the present invention, theTEM image of the silicon compound microporous particles can be observed,for example, by the method described below.

(Observation of Microporous Particle Using TEM)

In the present invention, the form of the silicon compound microporousparticle can be observed and analyzed using a transmission electronmicroscope (TEM). Specifically, a dispersion liquid of the siliconcompound microporous particle is diluted so as to obtain a solutionhaving an appropriate concentration, and the resultant is dispersed on acarbon support and dried to obtain a microporous particle sample. Then,the sample is observed using a TEM (product of Hitachi, Ltd., productname: H-7650, acceleration voltage: 100 kV), and an electron image canbe obtained with an observation magnification×100,000.

The particle size distribution showing particle size variations of thesilicon compound microporous particle is not limited to particularvalues. The distribution of the particle having a particle size of 0.4μm to 1 μm is, for example, 50 wt % to 99.9 wt %, 80 wt % to 99.8 wt %,or 90 wt % to 99.7 wt % or the distribution of the particle having aparticle size of 1 μm to 2 μm is 0.1 wt % to 50 wt %, 0.2 wt % to 20 wt%, or 0.3 wt % to 10 wt %, for example. The particle size distributioncan be measured, for example, using a particle size distributionanalyzer or an electron microscope.

The silicone porous body of the present invention may contain a catalystfor chemically bonding the silicon compound microporous particles, forexample. The content of the catalyst is not limited to particularvalues, and the content of the catalyst relative to the weight of thesilicon compound microporous particle is, for example, 0.01 wt % to 20wt %, 0.05 wt % to 10 wt %, or 0.1 wt % to 5 wt %.

The silicone porous body of the present invention may further contain acrosslinking assisting agent for indirectly bonding the silicon compoundmicroporous particles, for example. The content of the crosslinkingassisting agent is not limited to particular values, and the content ofthe crosslinking assisting agent relative to the weight of the siliconcompound microporous particle is, for example, 0.01 wt % to 20 wt %,0.05 wt % to 15 wt %, or 0.1 wt % to 10 wt %.

The form of the silicone porous body of the present invention is notlimited to particular forms, and can be, for example, in the form of afilm, a bulk body, or the like.

The method of producing a silicone porous body of the present inventionis not limited to particular methods, and the silicone porous body ofthe present invention can be produced, for example, by the productionmethod of the present invention described below.

[2. Production Method of Silicone Porous Body]

As described above, the method of producing a silicone porous body ofthe present invention includes steps of: preparing a liquid containingsilicon compound microporous particles, adding a catalyst for chemicallybonding the microporous particles to the liquid, and chemically bondingthe microporous particles by catalysis. The liquid containing thesilicon compound microporous particles is not limited to particularliquids, and can be, for example, a suspension containing the siliconcompound microporous particles. The silicon compound microporousparticle is preferably a pulverized product of a gelled silica compoundas described above. The production method is described below mainly withreference to the case where the silicon compound microporous particle isa pulverized product of a gelled silica compound (hereinafter, it may besimply referred to as a “pulverized product”). The method of producing asilicone porous body of the present invention, however, can be performedin the same manner also by using a fine particle other than thepulverized product of a gelled silica compound as the silicon compoundmicroporous particle. Besides the method of using the coating liquid,for example, a silicone porous body may be produced on a base by anaerosol deposition method (AD method) or the like in a dry environment.

The production method of the present invention can provide a siliconeporous body having a porous structure with less cracks and a highproportion of void space as well as having a sufficient strength. Thefollowing theory about the reason for this can be formed. The presentinvention, however, is not limited thereto.

Since the pulverized product used in the production method of thepresent invention is obtained by pulverizing the gelled siliconcompound, the three-dimensional structure of the gelled silicon compoundbefore pulverization is dispersed into three-dimensional basicstructures. In the production method of the present invention, thethree-dimensional basic structures are deposited using a sol containingthe pulverized products of the gelled silicon compound, and the porousstructure based on the three-dimensional basic structures is formed.That is, according to the production method of the present invention, anew porous structure is formed of the pulverized products each havingthe three-dimensional basic structure, which is different from thethree-dimensional structure of the gelled silicon compound. Moreover, inthe production method of the present invention, since the pulverizedproducts are chemically bonded, the new three-dimensional structure isimmobilized. Thus, the silicone porous body obtained by the productionmethod of the present invention, despite its structure with void spaces,can maintain a sufficient strength with less cracks. According to theproduction method of the present invention, for example, the siliconeporous body can be formed as a single bulk body, or the silicone porousbody can be formed as an additional member to various objects. Thesilicone porous body obtained by the present invention can be used, as amember utilizing voids, for products in a wide range of fields includingoptical elements such as low refractive index layers, heat insulatingmaterials, sound absorbing materials, regenerative medical bases, dewcondensation preventing materials, and ink image receiving members, andcan be used for a method of producing a laminated film having variousfunctions, for example.

Regarding the production method of the present invention, reference canbe made to the description as to the silicone porous body of the presentinvention unless otherwise stated. The present invention can be utilizedfor production of any gel according to applications and purposes, and isparticularly effective for production of a xerogel, for example. Asdescribed above, the silicone porous body of the present inventionachieves a high proportion of void space as in the case of an aerogeleven with a xerogel, for example.

Regarding the gelled silicon compound, the pulverized product thereof,the monomer silicon compound, and the silicon compound precursor in theproduction method of the present invention, reference can be made to thedescription as to the silicone porous body of the present invention.

The production method of the present invention includes a step ofpreparing a liquid containing the silicon compound microporous particles(preferably, sol containing the pulverized products of the gelledsilicon compound) as described above. The pulverized product can beobtained, for example, by pulverizing the gelled silicon compound. Bypulverization of the gelled silicon compound, as described above, thethree-dimensional structure of the gelled silicon compound is destroyedand dispersed into three-dimensional basic structures.

Generation of the gelled silicon compound by gelation of the siliconcompound and preparation of the pulverized product by pulverization ofthe gelled silicon compound are described below. The present invention,however, is not limited thereto.

The gelation of the silicon compound can be performed, for example, bybonding the monomer silicon compounds by a hydrogen bond or anintermolecular bond.

The monomer silicon compound can be, for example, a silicon compoundrepresented by the chemical formula (1) described in the description asto the silicone porous body of the present invention.

(R¹_(4-x)SiOH)_(x)  (1)

Since the silicon compound represented by the chemical formula (1) has ahydroxyl group, monomers in the chemical formula (1) can be bonded by ahydrogen bond or an intermolecular bond through their hydroxyl groups,for example.

The silicon compound may be the hydrolysate of the silicon compoundprecursor as described above, and may be generated by hydrolyzing thesilicon compound precursor represented by the chemical formula (2)described in the description as to the silicone porous body of thepresent invention, for example.

(R¹_(4-x)SiOR²)_(x)  (2)

The method of hydrolyzing the silicon compound precursor is not limitedto particular methods, and can be performed by a chemical reaction inthe presence of a catalyst, for example. Examples of the catalystinclude acids such as an oxalic acid and an acetic acid. The hydrolysisreaction can be performed, for example, by gradually dropping an oxalicacid aqueous solution to a mixture (for example, suspension) of thesilicon compound and dimethylsulfoxide to mix at room temperature, andstirring the resultant for about 30 minutes. In hydrolysis of thesilicon compound precursor, for example, by completely hydrolyzing thealkoxy group of the silicon compound precursor, gelation and agingthereafter and heating and immobilization after formation of avoid-provided structure can be achieved more efficiently.

The gelation of the monomer silicon compound can be performed, forexample, by a dehydration condensation reaction among the monomers. Thedehydration condensation reaction is preferably performed in thepresence of a catalyst, for example. Examples of the catalyst includedehydration condensation catalysts such as: acid catalysts including ahydrochloric acid, an oxalic acid, and a sulfuric acid; and basecatalysts including ammonia, potassium hydroxide, sodium hydroxide, andammonium hydroxide. The dehydration condensation catalyst isparticularly preferably a base catalyst.

In the dehydration condensation reaction, the amount of the catalyst tobe added to the monomer silicon compound is not limited to particularvalues, and is, for example, 0.1 to 10 mol, 0.05 to 7 mol, or 0.1 to 5mol per mol of the monomer silicon compound.

The gelation of the monomer silicon compound is preferably performed ina solvent, for example. The proportion of the silicon compound in thesolvent is not limited to particular values. Examples of the solventinclude dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), dimethylformamide (DMF), γ-butyrolactone(GBL), acetonitrile (MeCN), and ethylene glycol ethyl ether (EGEE). Oneof the solvents may be used alone or two or more of them may be used incombination, for example. Hereinafter, the solvent used for the gelationis also referred to as a “gelation solvent”.

The condition for the gelation is not limited to particular conditions.Regarding the solvent containing the silicon compound, the treatmenttemperature is, for example, 20° C. to 30° C., 22° C. to 28° C., or 24°C. to 26° C., and the treatment time is, for example, 1 to 60 minutes, 5to 40 minutes, or 10 to 30 minutes. In the case of performing thedehydration condensation reaction, the treatment condition is notlimited to particular conditions and reference can be made to theseexamples. By gelation, a siloxane bond is grown and silica primaryparticles are formed. As the reaction further proceeds, the primaryparticles are connected in the form of a string of beads to generate agel having a three-dimensional structure, for example.

The gelled silicon compound obtained by the gelation is preferablysubjected to aging treatment after the gelation reaction. The agingtreatment causes further growth of the primary particles of a gel havinga three-dimensional structure obtained by gelation, for example, andthis allows the size of the particle itself to be increased. As aresult, the contact state of the neck where particles are in contactwith each other can be increased from a point contact to a surfacecontact. The gel which has been subjected to the aging treatmentincreases its strength, for example, and this increases the strength ofthe three-dimensional basic structure after pulverization. Thisprevents, in the drying step after coating of the pulverized product,the pore size of the void-provided structure obtained by deposition ofthe three-dimensional basic structures from shrinking in accordance withsolvent volatilization during the drying process, for example.

The aging treatment can be performed, for example, by incubating thegelled silicon compound at a predetermined temperature for apredetermined time. The predetermined temperature is not particularlylimited, and the lower limit thereof is, for example, 30° C. or more,35° C. or more, or 40° C. or more, the upper limit thereof is, forexample, 80° C. or less, 75° C. or less, or 70° C. or less, and thepredetermined temperature is, for example, in the range from 30° C. to80° C., 35° C. to 75° C., or 40° C. to 70° C. The predetermined time isnot particularly limited, and the lower limit is, for example, 5 hoursor more, 10 hours or more, or 15 hours or more, the upper limit is, forexample, 50 hours or less, 40 hours or less, or 30 hours or less, andthe predetermined time is, for example, in the range from 5 hours to 50hours, 10 hours to 40 hours, or 15 hours to 30 hours. An optimalcondition for the aging is, for example, the condition mainly aiming forincrease in the size of the silica primary particle and increase in thecontact area of the neck. Furthermore, it is preferable to take theboiling point of a solvent to be used into consideration. For example,when the aging temperature is too high, there is a possibility that thesolvent excessively volatilizes, which causes defectiveness such thatthe pore of the three-dimensional void-provided structure closes due tothe condensation of the concentration of a coating liquid (gel liquid).On the other hand, for example, when the aging temperature is too low,there is a possibility not only that a sufficient effect of the aging isnot brought about but also that temperature variations over time in amass production process increase, which causes products with poorquality to be produced.

The same solvent as the solvent used in the gelation treatment can beused in the aging treatment, for example. Specifically, the agingtreatment is preferably applied to a reactant (the solvent containingthe gelled silicon) after the gelation treatment. The mol number ofresidual silanol groups contained in the gel (the gelled siliconcompound) after completion of the aging treatment after gelation is, forexample, the proportion of the residual silanol group with the molnumber of alkoxy groups of the added raw material (for example, thesilicon compound precursor) being considered as 100, and the upper limitthereof is, for example, 50% or less, 40% or less, or 30% or less, thelower limit thereof is, for example, 1% or more, 3% or more, or 5% ormore, and the mol number is, for example, in the range from 1% to 50%,3% to 40%, or 5% to 30%. For the purpose of increasing the hardness of agel, for example, the lower the mol number of the residual silanolgroups, the better. When the mol number of the silanol groups is toohigh, for example, there is a possibility that the void-providedstructure cannot be held until crosslinking is done in the precursors ofthe silicone porous body. On the other hand, when the mol number of thesilanol groups is too low, for example, there is a possibility that theprecursors of the silicone porous body cannot be crosslinked in thebonding step, which hinders a sufficient strength from being imparted.Note that while the aforementioned description is described withreference to a silanol group as an example, the same phenomenon shall beapplied to various functional groups when a monomer silicon compound ismodified with various reactive functional groups, for example.

After gelation of the monomer silicon compound in the gelation solvent,the obtained gelled silicon compound is pulverized. The gelled siliconcompound in the gelation solvent which has not been processed may bepulverized, or the gelation solvent may be substituted with anothersolvent and the gelled silicon compound in the substituted solvent maybe pulverized, for example. Furthermore, if the catalyst and solventused in the gelation reaction remain after the aging step, which causesgelation of the liquid over time (pot life) and decreases the dryingefficiency in the drying step, it is preferable to substitute thegelation solvent with another solvent. Hereinafter, this another solventmay be also referred to as a “pulverization solvent”.

The pulverization solvent is not limited to particular solvents, and canbe, for example, an organic solvent. The organic solvent can be, forexample, a solvent having a boiling point at 130° C. or less, 100° C. orless, or 85° C. or less. Specific examples of the organic solventinclude isopropyl alcohol (IPA), ethanol, methanol, butanol, propyleneglycol monomethyl ether (PGME), methyl cellosolve, acetone, anddimethylformamide (DMF). One of the pulverization solvents may be usedalone or two or more of them may be used in combination.

The combination of the gelation solvent and the pulverization solvent isnot limited to particular combinations, and the combination can be, forexample, the combination of DMSO and IPA, the combination of DMSO andethanol, the combination of DMSO and methanol, and the combination ofDMSO and butanol. Substitution of the gelation solvent with thepulverization solvent makes it possible to form a coating film withuniform quality in the coating film formation described below, forexample.

The method of pulverizing the gelled silicon compound is not limited toparticular methods, and a high pressure medialess pulverizing apparatusis preferably used. Examples of the apparatus for pulverizing include:wet-type medialess pulverizing apparatuses utilizing a cavitationphenomenon such as an ultrasonic homogenizer, a high-speed rotatinghomogenizer, and a high pressure extrusion pulverizing apparatus; andpulverizing apparatuses of causing oblique collision of liquids at ahigh pressure. An apparatus such as a ball mill that performs mediapulverization physically destroys the void-provided structure of a gelin pulverization, for example. On the other hand, a cavitation-typepulverizing apparatus such as a homogenizer, which is preferable in thepresent invention, peels the contact surface of silica sol particles,which are already contained in a gel three-dimensional structure andbonded relatively weakly, with a high pressure and a high speed shearingforce by a medialess method without causing physical destructionphenomenon of a medium. Thus, a sol three-dimensional structure to beobtained can hold the void-provided structure having a particle sizedistribution of a certain range of a submicron region and can form thevoid-provided structure again by deposition in coating and drying, forexample. The condition for the pulverization is not limited toparticular conditions, and is preferably a condition that allows a gelto be pulverized without volatilizing a solvent by instantaneouslyimparting a high speed flow, for example. For example, it is preferableto pulverize the gelled silicon compound so as to obtain pulverizedproducts having the above described particle size variations (forexample, volume average particle size or particle size distribution). Ifthe pulverization time, the pulverization strength, or the like islacking, for example, there is a possibility not only that coarseparticles remain, which hinders dense pores from being formed but alsothat defects in appearance increase, which hinders high quality frombeing achieved. On the other hand, if the pulverization time, thepulverization strength, or the like is too much, for example, there is apossibility that a finer sol particle than a desired particle sizedistribution is obtained and the size of a void space deposited aftercoating and drying is too fine to satisfy a desired porosity.

In the manner described above, a liquid (for example, suspension)containing the microporous particles (pulverized products of a gelledsilicon compound) can be prepared. By further adding a catalyst forchemically bonding the microporous particles after or during thepreparation of the liquid containing the microporous particles, a liquidcontaining the microporous particles and the catalyst can be prepared.The amount of the catalyst to be added is not limited to particularvalues, and the amount of the catalyst to be added relative to theweight of the microporous particle (pulverized product of the gelledsilicon compound) is, for example, in the range from 0.01 wt % to 20 wt%, 0.05 wt % to 10 wt %, or 0.1 wt % to 5 wt %. This catalyst chemicallybonds the microporous particles in the bonding step described below, forexample. The catalyst may be, for example, a catalyst that promotes thecrosslinking bond among the microporous particles. As the chemicalreaction of chemically bonding the microporous particles, it ispreferable to utilize the dehydration condensation reaction of aresidual silanol group contained in a silica sol molecule. By promotingthe reaction between the hydroxyl groups of the silanol group by thecatalyst, the continuous formation of a film in which the void-providedstructure is cured in a short time can be performed. Examples of thecatalyst include photoactive catalysts and thermoactive catalysts. Thephotoactive catalyst allows the chemical bond (for example, crosslinkingbond) among the microporous particles without heating, for example. Thismakes it possible to maintain a higher proportion of void space becausethe shrinkage due to heating is less liable to occur, for example. Inaddition to or instead of the catalyst, a substance (catalyst generator)that generates a catalyst may be used. For example, the catalyst may bea crosslinking reaction accelerator and the catalyst generator may be asubstance that generates the crosslinking reaction accelerator. Forexample, in addition to or instead of the photoactive catalyst, asubstance (photocatalyst generator) that generates a catalyst by lightirradiation may be used. For example, in addition to or instead of thethermoactive catalyst, a substance (thermal catalyst generator) thatgenerates a catalyst by heating may be used. The photocatalyst generatoris not limited to particular photocatalyst generators, and examplesthereof include photobase generators (substances that generate basiccatalysts by light irradiation) and photoacid generators (substancesthat generate acidic catalysts by light irradiation). Among them, thephotobase generator is preferable. Examples of the photobase generatorinclude 9-anthrylmethyl N, N-diethylcarbamate (product name: WPBG-018),(E)-1-[3-(2-hydroxyphenyl)-2-propenoyl]piperidine (product name:WPBG-027), 1-(anthraquinon-2-yl)ethyl imidazolecarboxylate (productname: WPBG-140), 2-nitrophenylmethyl4-methacryloyloxypiperidine-1-carboxylate (product name: WPBG-165),1,2-diisopropyl-3-[bis(dimethylamino) methylene]guanidium2-(3-benzoylphenyl)propionate (product name: WPBG-266),1,2-dicyclohexyl-4,4,5,5-tetramethylbiguanidium n-butyltriphenylborate(product name: WPBG-300), 2-(9-oxoxanthen-2-yl)propionic acid1,5,7-triazabicyclo[4.4.0] dec-5-ene (Tokyo Kasei Kogyo Co., Ltd.), anda compound containing 4-piperidinemethanol (product of Heraeus, productname: HDPD-PB100). Note here that each product with the name including“WPBG” is a product of Wako Pure Chemical Industries, Ltd. Examples ofthe photoacid generator include aromatic sulfonium salt (product ofADEKA, product name: SP-170), triarylsulfonium salt (product of San-AproLtd., product name: CPI101A), and aromatic iodonium salt (product ofCiba Japan, product name: Irgacure 250). The catalyst for chemicallybonding the microporous particles is not limited to the photoactivecatalyst and the photocatalyst generator, and can be, for example, athermoactive catalyst or a thermal catalyst generator such as urea.Examples of the catalyst for chemically bonding the microporousparticles include base catalysts such as potassium hydroxide, sodiumhydroxide, and ammonium hydroxide; and acid catalysts such as ahydrochloric acid, an acetic acid, and an oxalic acid. Among them, thebase catalyst is preferable. The catalyst for chemically bonding themicroporous particles can be used by adding it to a sol particle liquid(for example, suspension) containing the pulverized products(microporous particles) right before the coating, or the catalyst can beused as a mixture by mixing it with a solvent, for example. The mixturemay be, for example, a coating liquid obtained by adding the catalystdirectly to the sol particle liquid, a solution obtained by dissolvingthe catalyst in a solvent, or a dispersion liquid obtained by dispersingthe catalyst into a solvent. The solvent is not limited to particularsolvents, and examples thereof include various organic solvents, water,and buffer solutions.

For example, in the case where the silicon compound microporous particleis a pulverized product of a gelled silicon compound obtained from asilicon compound containing at least three or less functional groupshaving saturated bonds, a crosslinking assisting agent for indirectlybonding the silicon compound microporous particles may further be addedafter or during preparation of a liquid containing the silicon compoundmicroporous particles. This crosslinking assisting agent penetratesamong particles and interacts with or bonds to the particles, whichhelps to bond particles relatively distanced from one another and makesit possible to increase the strength efficiently. As the crosslinkingassisting agent, a multicrosslinking silane monomer is preferable.Specifically, the multicrosslinking silane monomer may have at least twoand at most three alkoxysilyl groups, the chain length between thealkoxysilyl groups may be 1-10 C, and the multicrosslinking silanemonomer may contain an element other than carbon, for example. Examplesof the crosslinking assisting agent include bis(trimethoxysilyl)ethane,bis(triethoxysilyl)ethane, bis(trimethoxysilyl)methane,bis(triethoxysilyl)methane, bis(triethoxysilyl)propane,bis(trimethoxysilyl)propane, bis(triethoxysilyl)butane,bis(trimethoxysilyl)butane, bis(triethoxysilyl)pentane,bis(trimethoxysilyl)pentane, bis(triethoxysilyl)hexane,bis(trimethoxysilyl)hexane,bis(trimethoxysilyl)-N-butyl-N-propyl-ethane-1,2-diamine,tris-(3-trimethoxysilylpropyl)isocyanurate, andtris-(3-triethoxysilylpropyl)isocyanurate. The amount of thecrosslinking assisting agent to be added is not limited to particularvalues, and the amount of the crosslinking assisting agent to be addedrelative to the weight of the silicon compound microporous particle is,for example, in the range from 0.01 wt % to 20 wt %, 0.05 wt % to 15 wt%, or 0.1 wt % to 10 wt %.

The silicone porous body can be formed by forming a coating film using aliquid containing the silicon compound microporous particles(preferably, sol containing pulverized products of the gelled siliconcompound), for example. The coating of the base with the siliconcompound microporous particles can be performed, for example, by thevarious coating methods described below but not limited thereto. Bydirectly coating the base with the solvent containing the pulverizedproducts, the coating film can be formed. The precursor of the porousbody, which is the coating film before the bonding step described below,can be also referred to as a precursor film (or precursor layer) of thesilicone porous body of the present invention, for example. Formation ofthe coating film causes the settlement and deposition of the pulverizedproduct whose three-dimensional structure has been destroyed, forexample, and this allows a new three-dimensional structure to be formed.

The solvent (hereinafter, also referred to as a “coating solvent”) isnot limited to particular solvents, and can be, for example, an organicsolvent. The organic solvent can be, for example, a solvent having aboiling point at 130° C. or less. Specific examples of the solventinclude IPA, ethanol, methanol, and butanol, and the examples of thepulverization solvent described above can be used. In the case where thepresent invention includes a step of pulverizing the gelled siliconcompound, for example, the pulverization solvent containing thepulverized products of the gelled silicon compound can be used withoutprocessing in the coating film forming step.

In the coating film forming step, for example, it is preferable to coatthe base with the sol silicon compound microporous particles dispersedin the solvent (hereinafter, referred to as a “sol particle liquid”).After coating the base with the sol particle liquid of the presentinvention and drying it, by chemically crosslinking the particles in thebonding step, the continuous formation of a void-provided layer having astrength of a certain level or more can be performed. The “sol” in thepresent invention denotes a fluidic state in which silica sol particleseach having a nano three-dimensional structure holding a part of thevoid-provided structure are dispersed in a solvent by pulverization ofthe three-dimensional structure of a gel.

The concentration of the silicon compound microporous particle in thesolvent is not limited to particular values, and is, for example, in therange from 0.3% to 80% (v/v), 0.5% to 40% (v/v), or 1.0% to 10% (v/v).When the concentration of the pulverized product is too high, there is apossibility that the fluidity of the sol particle liquid decreasessignificantly, which causes aggregates and coating stripes in coating,for example. On the other hand, when the concentration of the siliconcompound microporous particle is too low, there is a possibility notonly that the drying of the sol particle solvent takes a relatively longtime but also that the residual solvent right after the dryingincreases, which may decrease the porosity, for example.

There is no particular limitation on the physical property of the solparticle liquid. The shear viscosity of the sol particle liquid is, forexample, 100 cPa·s or less, 10 cPa·s or less, or 1 cPa·s or less, forexample, at the shear rate of 10001/s. When the shear viscosity is toohigh, for example, there is a possibility that the coating stripes aregenerated, which causes defectiveness such as decrease in the transferrate in the gravure coating. In contrast, when the shear viscosity istoo low, for example, there is a possibility that the thickness of thewet coating during coating cannot be increased and a desired thicknesscannot be obtained after drying.

The coating amount of the silicon compound microporous particle relativeto the base is not limited to particular values, and can be determinedappropriately, for example, according to the thickness of a desiredsilicone porous body. As a specific example, in the case of forming thesilicone porous body having a thickness of 0.1 to 1000 μm, the coatingamount of the pulverized product relative to the base is, for example,in the range from 0.01 to 60000 g, 0.1 to 5000 g, or 1 to 50 g persquare meter of the base. Although it is difficult to uniquely define apreferable coating amount of the sol particle liquid because it dependson the concentration of a liquid, the coating method, or the like, forexample, it is preferable that a coating layer is as thin as possible inconsideration of productivity. When the coating amount is too much, forexample, there is a high possibility that a solvent is dried in a dryingoven before volatilizing. When the solvent is dried before forming thevoid-provided structure by the settlement and deposition of the nanopulverized sol particles in the solvent, there is a possibility thatformation of void spaces is inhibited and the proportion of void spacedecreases. On the other hand, when the coating amount is too little,there is a possibility of increasing the risk of causing coating cissingdue to unevenness of a base, variations in hydrophilicity andhydrophobicity, and the like.

After coating the base with the pulverized product, drying treatment maybe applied to the coating film. The drying treatment of the presentinvention is characterized in that the treatment can be applied from arelatively low temperature, and is suitable for a quick continuousproduction. The drying treatment is aimed not only for removing thesolvent (solvent contained in the sol particle liquid) from the coatingfilm but also for causing the settlement and deposition of the solparticles to form a void-provided structure in the drying treatment, forexample. The temperature for the drying treatment is, for example, inthe range from 50° C. to 200° C., 60° C. to 150° C., or 70° C. to 130°C., and the time for the drying treatment is, for example, in the rangefrom 0.1 to 30 minutes, 0.2 to 10 minutes, or 0.3 to 3 minutes.Regarding the temperature and time for the drying treatment in relationto continuous productivity and high porosity expression, the lower thebetter and the shorter the better, for example. When the condition istoo strict, there is a possibility of causing the following problems,for example. That is, when the base is a resin film, for example, thebase extends in a drying oven as the temperature approaches theglass-transition temperature of the base, which causes defects such ascracks in a formed void-provided structure right after coating. On theother hand, when the condition is too mild, there is a possibility ofcausing the following problems, for example. That is, since the filmcontains a residual solvent when it comes out of the drying oven,defects in appearance such as scratches are caused when the film rubsagainst a roller in the next step.

The drying treatment may be, for example, natural drying, drying byheating, or drying under reduced pressure. There is no particularlimitation on the drying method and a common heating unit can be used,for example. Examples of the heating unit include a hot air fan, aheating roll, and a far-infrared heater. Among them, in view ofperforming continuous production industrially, drying by heating ispreferable. The solvent to be used is preferably a solvent having a lowsurface tension in view of reducing the shrinkage stress in accordancewith the solvent volatilization in drying and reducing the crackphenomenon of the void-provided layer (the silicone porous body) due tothe shrinkage stress. The solvent can be, for example, lower alcoholtypified by isopropyl alcohol (IPA), hexane, perfluorohexane, and thelike. The solvent, however, is not limited thereto. The temperature andtime for the drying treatment can be changed depending on the thicknessof an intended silanol porous body, the type of the solvent, and thelike.

The base is not limited to particular bases, and a porous body having nobase and a porous body formed on a base can be formed properly dependingon the configuration of an intended silanol porous body. For example, abase made of thermoplastic resin, a base made of glass, an inorganicbase typified by silicon, plastic molded using thermosetting resin orthe like, an element such as a semiconductor, a carbon fiber materialtypified by carbon nanotube, or the like can be preferably used. Thebase, however, is not limited thereto. Examples of the form of the baseinclude a film and a plate. Examples of thermoplastic resin includebases having high transparency such as polyethylene terephthalate (PET),acryl, cellulose acetate propionate (CAP), cycloolefin polymer (COP),triacetate (TAC), polyethylene naphthalate (PEN), polyethylene (PE), andpolypropylene (PP).

In the production method of the present invention, the bonding step is astep of chemically bonding the silicon compound microporous particlescontained in the coating film, and either wet-type treatment or dry-typetreatment will do. The three-dimensional structure of the siliconcompound microporous particle in the precursor of the porous body isimmobilized in the bonding step, for example. In the case ofimmobilizing the three-dimensional structure by conventional sintering,for example, the dehydration condensation of a silanol group and theformation of a siloxane bond are induced by high temperature treatmentat 200° C. or more. In the bonding step of the present invention, forexample, when a base is a resin film, wet-type treatment can beperformed at about 100° C. which is relatively low for less than severalminutes which is short without damaging the base by causing variousadditives, which catalyze the dehydration condensation reaction, toreact. Ultraviolet irradiation may be performed after the drying step toconduct a bonding reaction by quick dry-type treatment utilizingphotocatalysis, and this allows the void-provided structure to be formedand immobilized continuously. The wet-type treatment is advantageous inthat it only needs a hot air drying step because it causes acrosslinking reaction while forming the coating film, whereas isdisadvantageous in that a high proportion of void space is less likelyachieved because it causes a crosslinking reaction while forming thevoid-provided structure. The same kinds of phenomena are expected alsoin the case of causing the bonding reaction by immersing a formedvoid-provided structure in a catalyst solution. On the other hand, thedry-type treatment, which causes a crosslinking reaction after forming ahigh void-provided structure of a silanol precursor (two-step reaction),is advantageous in that formation of a high void-provided structure isless likely inhibited. It is preferable to properly use the wet-typetreatment and the dry-type treatment according to the purpose.

The method of chemically bonding the particles is not limited toparticular methods, and can be determined appropriately according to thetype of the gelled silicon compound, for example. Specifically, forexample, the chemical bond can be a chemical crosslinking bond among thesilicon compound microporous particles. Besides this, for example, wheninorganic particles such as titanium oxide particles are added to thesilicon compound microporous particles, the inorganic particles and thesilicon compound microporous particles can be chemically bonded bycrosslinking.

Furthermore, there are a case of using a biocatalyst such as an enzymeand a case of chemically crosslinking the pulverized product and acatalyst at a site which is different from a catalytic activity site.Thus, the present invention can be applied not only to a void-providedlayer (silicone porous body) formed of the sol particles but also to anorganic-inorganic hybrid void-provided layer, a host-guest void-providedlayer, and the like, for example. The present invention, however, is notlimited thereto.

The bonding step can be carried out by a chemical reaction in thepresence of a catalyst according to the type of the silicon compoundmicroporous particle, for example. The chemical reaction in the presentinvention is preferably a reaction utilizing a dehydration condensationreaction of a residual silanol group contained in a silica sol molecule.By promoting the reaction between the hydroxyl groups of the silanolgroup by the catalyst, the continuous formation of a film in which thevoid-provided structure is cured in a short time can be performed.Silicon monomer materials organically modified with other reactivefunctional groups however may be used as silica gel materials, and thefunctional group reacted in the bonding step is not limited to thesilanol group. Examples of the catalyst include base catalysts such aspotassium hydroxide, sodium hydroxide, and ammonium hydroxide, and acidcatalysts such as a hydrochloric acid, an acetic acid, and an oxalicacid. The catalyst, however, is not limited thereto. The catalyst usedin the dehydration condensation reaction is preferably a base catalyst.Furthermore, photoacid generation catalysts, photobase generationcatalysts, photoacid generators, photobase generators, and the like,each of which expresses a catalytic activity by light (for example,ultraviolet) irradiation, may preferably be used. The photoacidgeneration catalysts, photobase generation catalysts, photoacidgenerators, and photobase generators are not limited to particularcatalysts, and can be, for example, as described above. Preferably, asdescribed above, the catalyst is used by adding it to a sol particleliquid containing the pulverized products right before the coating orthe catalyst is used as a mixture by mixing it with a solvent, forexample. The mixture may be, for example, a coating liquid obtained byadding the catalyst directly to the sol particle liquid, a solutionobtained by dissolving the catalyst in a solvent, or a dispersion liquidobtained by dispersing the catalyst into a solvent. The solvent is notlimited to particular solvents as described above, and examples thereofinclude various organic solvents, water, and buffer solutions.

The chemical reaction in the presence of the catalyst can be performed,for example, by heating the coating film containing the catalystpreliminarily added to the sol particle liquid or irradiating thecoating film containing the catalyst preliminarily added to the solparticle liquid with light, by heating the coating film or irradiatingthe coating film with light after the catalyst has been sprayed to thecoating film, or by heating the coating film or irradiating the coatingfilm with light while spraying the catalyst to the coating film. Forexample, when the catalyst is a photoactive catalyst, the porous bodycan be formed by chemically bonding the microporous particles by lightirradiation. When the catalyst is a thermoactive catalyst, the porousbody can be formed by chemically bonding the microporous particles byheating. The accumulated light amount in the light irradiation is notlimited to particular values, and is, for example, 200 to 800 mJ/cm²,250 to 600 mJ/cm², or 300 to 400 mJ/cm² in terms of the wave length of360 nm. From the view point of preventing the effect from beinginsufficient due to the delay of decomposition of the catalyst by lightabsorption because of insufficient irradiation amount, the accumulatedlight amount is preferably 200 mJ/cm² or more. From the view point ofpreventing heat wrinkles from generating due to the damage on a basebelow a void-provided layer, the accumulated light amount is preferably800 mJ/cm² or less. The conditions for the heat treatment are notlimited to particular conditions. The heating temperature is, forexample, 50° C. to 250° C., 60° C. to 150° C., or 70° C. to 130° C., theheating time is, for example, 0.1 to 30 minutes, 0.2 to 10 minutes, or0.3 to 3 minutes. The solvent to be used is preferably a solvent havinga low surface tension in view of reducing the shrinkage stress inaccordance with the solvent volatilization in drying and reducing thecrack phenomenon of the void-provided layer due to the shrinkage stress,for example. The solvent can be, for example, lower alcohol typified byisopropyl alcohol (IPA), hexane, perfluorohexane, or the like. Thesolvent, however, is not limited thereto. For example, the surfacetension of the solvent may be reduced by adding a small amount ofperfluoro surfactant or silicon surfactant to the IPA.

In the manner described above, the silicone porous body of the presentinvention can be produced. The production method of the presentinvention, however, is not limited thereto.

The thus obtained silicone porous body of the present invention may besubjected to a strength increasing step (hereinafter, also referred toas an “aging step”) of applying thermal aging to increase the strength,for example. For example, when the silicone porous body of the presentinvention is stacked on a resin film, the peel strength to the resinfilm can be increased by the strength increasing step (aging step). Inthe strength increasing step (aging step), for example, the siliconeporous body of the present invention may be heated. The temperature ofthe aging step is, for example, 40° C. to 70° C., 45° C. to 65° C., or50° C. to 60° C. The time for the aging step is, for example, 10 to 30hours, 13 to 25 hours, or 15 to 20 hours. By setting the heatingtemperature low in the aging step, for example, the peel strength can beincreased while reducing the shrinkage of the silicone porous body,thereby achieving both a high proportion of void space and a strength.

While the phenomenon and mechanism caused in the strength increasingstep (aging step) are unknown, for example, it is considered that thecatalyst contained in the silicone porous body of the present inventionpromotes the chemical bond (for example, crosslinking reaction) amongthe microporous particles, thereby increasing the strength. As aspecific example, when the microporous particles are silicon compoundmicroporous particles (for example, pulverized products of a gelledsilica compound) and residual silanol groups (OH groups) are present inthe silicone porous body, it is considered that the residual silanolgroups are chemically bonded by a crosslinking reaction. The catalystcontained in the silicone porous body of the present invention is notlimited to particular catalysts, and can be, for example, a catalystused in the bonding step, a basic substance generated by the photobasegeneration catalyst used in the bonding step by light irradiation, or anacidic substance generated by the photoacid generation catalyst used inthe bonding step by light irradiation. The description, however, isillustrative and does not limit the present invention.

A pressure-sensitive adhesive/adhesive layer may additionally be formedon the silicone porous body of the present invention (pressure-sensitiveadhesive/adhesive layer forming step). Specifically, for example, thepressure-sensitive adhesive/adhesive layer may be formed by applying apressure-sensitive adhesive or an adhesive to the silicone porous bodyof the present invention. The pressure-sensitive adhesive/adhesive layermay be formed on the silicone porous body of the present invention usingan adhesive tape in which the pressure-sensitive adhesive/adhesive layerstacked on a base by adhering the pressure-sensitive adhesive/adhesivelayer side of the adhesive tape on the silicone porous body of thepresent invention. In this case, the base of the adhesive tape may bekept adhered or peeled from the pressure-sensitive adhesive/adhesivelayer. In the present invention, a “pressure-sensitive adhesive” and a“pressure-sensitive adhesive layer” are used based on the premise thatan adherend is re-peelable, for example. In the present invention, an“adhesive” and an “adhesive layer” are used based on the premise that anadherend is not re-peelable, for example. In the present invention,however, the “pressure-sensitive adhesive” and the “adhesive” are notalways distinguishable and the “pressure-sensitive adhesive layer” andthe “adhesive layer” are not always distinguishable. In the presentinvention, there is no particular limitation on the pressure-sensitiveadhesives or the adhesives for forming the pressure-sensitiveadhesive/adhesive layer, and a common pressure-sensitive adhesive oradhesive can be used, for example. Examples of the pressure-sensitiveadhesive and the adhesive include polymer adhesives such as acrylicadhesives, vinyl alcohol adhesives, silicone adhesives, polyesteradhesives, polyurethane adhesives, and polyether adhesives; and rubberadhesives. Furthermore, the pressure-sensitive adhesive and the adhesivecan be an adhesive including a water-soluble crosslinking agent of vinylalcohol polymer such as glutaraldehyde, melamine, or an oxalic acid. Onetype of the pressure-sensitive adhesives and adhesives may be used aloneor two or more types of them may be used in combination (for example,mixing, lamination, and the like). The thickness of thepressure-sensitive adhesive/adhesive layer is not limited to particularvalues, and is, for example, 0.1 to 100 μm, 5 to 50 μm, 10 to 30 μm, or12 to 25 μm.

Furthermore, an intermediate layer may be formed between the siliconeporous body of the present invention and the pressure-sensitiveadhesive/adhesive layer by causing the silicone porous body of thepresent invention to react with the pressure-sensitive adhesive/adhesivelayer (intermediate layer forming step). Owing to the intermediatelayer, the silicone porous body of the present invention and thepressure-sensitive adhesive/adhesive layer are not easily peeled fromeach other, for example. reason (mechanism) for this is unknown, it ispresumed that the silicone porous body of the present invention and thepressure-sensitive adhesive/adhesive layer are not easily peeled fromeach other owing to the anchoring property (anchor effect) of theintermediate layer, for example. The anchoring property (anchor effect)is a phenomenon (effect) that the interface between the void-providedlayer and the intermediate layer is strongly fixed because theintermediate layer is entangled in the void-provided layer in thevicinity of the interface. This reason (mechanism), however, is anexample of a presumable reason (mechanism), and does not limit thepresent invention. The reaction between the silicone porous body of thepresent invention and the pressure-sensitive adhesive/adhesive layer isnot limited to particular reactions, and can be, for example, a reactionby catalysis. The catalyst may be a catalyst contained in the siliconeporous body of the present invention, for example. Specifically, thecatalyst can be, for example, a catalyst used in the bonding step, abasic substance generated by the photobase generation catalyst used inthe bonding step by light irradiation, or an acidic substance generatedby the photoacid generation catalyst used in the bonding step by lightirradiation. The reaction between the silicone porous body of thepresent invention and the pressure-sensitive adhesive/adhesive layer maybe, for example, a reaction (for example, crosslinking reaction) thatgenerates a new chemical bond. The temperature of the reaction is, forexample, 40° C. to 70° C., 45° C. to 65° C., or 50° C. to 60° C. Thetime for the aging step is, for example, 10 to 30 hours, 13 to 25 hours,or 15 to 20 hours. This intermediate layer forming step may also serveas the strength increasing step (aging step) of increasing the strengthof the silicone porous body of the present invention.

The thus obtained silicone porous body of the present invention mayfurther be stacked on another film (layer) to form a laminate having theporous structure, for example. In this case, the components of thelaminate may be stacked through a pressure-sensitive adhesive or anadhesive, for example.

The components may be stacked by continuous treatment (so called Roll toRoll) using a long film, for example, in terms of efficiency. When thebase is a molded product, an element, or the like, the base that hasbeen subjected to a batch process may be stacked.

The method of forming the silicone porous body of the present inventionon a base is described below with reference to a continuous treatmentprocess using FIGS. 1 to 3 as an example. FIG. 2 shows a step ofadhering a protective film to a formed film of the silicone porous bodyand winding the laminate. In the case of stacking the silicone porousbody on another functional film, the aforementioned method may beadopted or the formed film of the silicone porous body may be adhered toanother functional film that has been coated and dried, right beforewinding. The method of forming a film shown in FIG. 2 is an example, andthe present invention is not limited thereto.

FIG. 1 is a cross sectional view schematically showing an example of theprocess of forming the silicone porous body on the base. In FIG. 1, themethod of forming a silicone porous body includes: (1) a coating step ofcoating a base 10 with a sol particle liquid 20″ containing siliconcompound microporous particles; (2) a coating film forming step (dryingstep) of drying the sol particle liquid 20″ to form a coating film 20′which is a precursor layer of the silicone porous body; and (3) achemical treatment step (for example, a crosslinking treatment step) ofapplying chemical treatment (for example, crosslinking treatment) to thecoating film 20′ to form a silicone porous body 20. In this manner, asshown in FIG. 1, the silicone porous body 20 can be formed on the base10. The method of forming a silicone porous body may include steps otherthan the steps (1) to (3) appropriately.

In the coating step (1), the method of coating the base with the solparticle liquid 20″ is not limited to particular methods, and a commonmethod can be adopted. Examples of the method include a slot die method,a reverse gravure coating method, a micro-gravure method (micro-gravurecoating method), a dip method (dip coating method), a spin coatingmethod, a brush coating method, a roller coating method, a flexography,a wire-bar coating method, a spray coating method, an extrusion coatingmethod, a curtain coating method, and a reverse coating method. Amongthem, from the viewpoint of productivity, smoothness of a coating film,and the like, an extrusion coating method, a curtain coating method, aroller coating method, a micro-gravure coating method, and the like arepreferable. The coating amount of the sol particle liquid 20″ is notlimited to particular values, and can be determined appropriately so asto obtain a porous structure (silicone porous body) 20 having anappropriate thickness, for example. The thickness of the porousstructure (silicone porous body) 20 is not limited to particular values,and is, for example, as described above.

In the (2) drying step, the sol particle liquid 20″ is dried (i.e.,dispersion medium contained in sol particle liquid 20″ is removed) toform a coating film (precursor layer) 20′. There is no particularlimitation on the condition for the drying treatment, and is asdescribed above.

In the (3) chemical treatment step, the coating film 20′ containing thecatalyst (for example, photoactive catalyst or thermoactive catalystsuch as KOH) which has been added before coating is irradiated withlight or heated to chemically bond (for example, crosslink) thepulverized products in the coating film (precursor) 20′, thereby forminga silicone porous body 20. The conditions for the light irradiation andheating in the (3) chemical treatment step are not limited to particularconditions, and are as described above.

FIG. 2 schematically shows an example of a slot die coating apparatusand an example of the method of forming a silicone porous body using thesame. Although FIG. 2 is a cross sectional view, hatching is omitted forviewability.

As shown in FIG. 2, the steps of the method using this apparatus arecarried out while carrying a base 10 in one direction by rollers. Thecarrying speed is not limited to particular values, and is, for example,in the range from 1 to 100 m/min, 3 to 50 m/min, or 5 to 30 m/min.

First, the base 10 is delivered from a delivery roller 101 and carriedto a coating roller 102, and the (1) coating step of coating the base 10with a sol particle liquid 20″ is carried out using the coating roller102. Subsequently, the (2) drying step is carried out in an oven zone110. In the coating apparatus shown in FIG. 2, a predrying step iscarried out after the (1) coating step and before the (2) drying step.The predrying step can be carried out at room temperature withoutheating. In the (2) drying step, a heating unit 111 is used. As theheating unit 111, as described above, a hot air fan, a heating roll, afar-infrared heater, or the like can be used appropriately. For example,the (2) drying step may be divided into multiple steps, and the dryingtemperature may be set higher as coming to later steps.

The (3) chemical treatment step is carried out in a chemical treatmentzone 120 after the (2) drying step. In the (3) chemical treatment step,for example, when the coating film 20′ after drying contains aphotoactive catalyst, light is emitted from lamps (light irradiationunits) 121 disposed above and below the base 10. On the other hand, forexample, when the coating film 20′ after drying contains a thermoactivecatalyst, the base 10 is heated using hot air fans 121 disposed aboveand below the base 10 instead of using the lamps (light irradiationdevices) 121. By this crosslinking treatment, the pulverized products inthe coating film 20′ are chemically bonded, and the silicone porous body20 is cured and strengthened. Instead of the hot air fans, ultravioletirradiators can be preferably used. After the (3) chemical treatmentstep, a laminate in which the silicone porous body 20 is formed on thebase 10 is wound by a winding roller 105. In FIG. 2, the silicone porousbody 20, which is a laminate, is protected by coating with a protectingsheet delivered from a roller 106. Instead of the protecting sheet,another layer formed of a long film may be stacked on the porousstructure 20.

FIG. 3 schematically shows an example of a micro-gravure coatingapparatus and an example of the method of forming a porous structureusing the same. Although FIG. 3 is a cross sectional view, hatching isomitted for viewability.

As shown in FIG. 3, the steps of the method using this apparatus arecarried out while carrying the base 10 in one direction by rollers as inFIG. 2. The carrying speed is not limited to particular values, and is,for example, in the range from 1 to 100 m/min, 3 to 50 m/min, or 5 to 30m/min.

First, the (1) coating step of coating the base 10 with a sol particleliquid 20″ is carried out while carrying the base 10 delivered from adelivery roller 201. As shown in FIG. 3, the coating with the solparticle liquid 20″ is performed using a liquid reservoir 202, a doctor(doctor knife) 203, and a micro-gravure 204. Specifically, the solparticle liquid 20″ in the liquid reservoir 202 is applied to thesurface of the micro-gravure 204 and the coating of the surface of thebase 10 is performed using the micro-gravure 204 while controlling thethickness to a predetermined thickness using a doctor 203. Themicro-gravure 204 is merely illustrative. The present invention is notlimited thereto, and any other coating unit may be adopted.

Subsequently, the (2) drying step is performed. Specifically, as shownin FIG. 3, the base 10 coated with the sol particle liquid 20″ iscarried into an oven zone 210 and dried by heating using heating units211 disposed in the oven zone 210. The heating units 211 can be, forexample, the same as those shown in FIG. 2. For example, the (2) dryingstep may be divided into multiple steps by dividing the oven zone 210into multiple sections, and the drying temperature may be set higher ascoming to later steps. The (3) chemical treatment step is carried out ina chemical treatment zone 220 after the (2) drying step. In the (3)chemical treatment step, for example, when the coating film 20′ afterdrying contains a photoactive catalyst, light is emitted from lamps(light irradiation units) 221 disposed above and below the base 10. Onthe other hand, for example, when the coating film 20′ after dryingcontains a thermoactive catalyst, the base 10 is heated using hot airfans (heating units) 221 disposed below the base 10 instead of using thelamps (light irradiation devices) 221. By this crosslinking treatment,the pulverized products in the coating film 20′ are chemically bonded,and the silicone porous body 20 is formed.

After the (3) chemical treatment step, a laminate in which the siliconeporous body 20 is formed on the base 10 is wound by a winding roller251. Thereafter, for example, another layer may be stacked on thelaminate. Furthermore, another layer may be stacked on the laminatebefore winding the laminate by the winding roller 251, for example.

FIGS. 6 to 8 show another example of a continuous treatment process offorming a silicone porous body of the present invention. As shown in thecross sectional view of FIG. 6, this method is the same as the methodshown in FIGS. 1 to 3 except that (4) strength increasing step (agingstep) is carried out after the (3) chemical treatment step (for example,crosslinking treatment step) of forming a silicone porous body 20. Asshown in FIG. 6, the strength of the silicone porous body 20 isincreased in the (4) strength increasing step (aging step), therebyforming a silicone porous body 21 with a greater strength. There is noparticular limitation on the (4) strength increasing step (aging step),and can be, for example, as described above.

FIG. 7 is a schematic view showing an example of a slot die coatingapparatus and an example of the method of forming a silicone porous bodyusing the same, which are different from those shown in FIG. 2. As canbe seen, the coating apparatus shown in FIG. 7 is the same as theapparatus shown in FIG. 2 except that the apparatus shown in FIG. 7includes a strength increasing zone (aging zone) 130 where the (4)strength increasing step (aging step) is carried out right next to thechemical treatment zone 120 where the (3) chemical treatment step iscarried out. That is, after the (3) chemical treatment step, the (4)strength increasing step (aging step) is carried out in the strengthincreasing zone (aging zone) 130 to increase the peel strength of thesilicone porous body 20 relative to a resin film 10, thereby forming asilicone porous body 21 having a higher peel strength. The (4) strengthincreasing step (aging step) may be carried out by heating the siliconeporous body 20 in the same manner as described above using hot air fans(heating units) 131 disposed above and below the base 10, for example.The conditions including the heating temperature, the time, and the likeare not limited to particular values, and can be, for example, asdescribed above. After the (4) strength increasing step, similar to theprocess shown in FIG. 3, a laminated film in which the silicone porousbody 21 is formed on the base 10 is wound by a winding roller 105.

FIG. 8 is a schematic view showing an example of a micro-gravure coatingapparatus and an example of the method of forming a porous structureusing the same, which are different from those shown in FIG. 3. As canbe seen, the coating apparatus shown in FIG. 8 is the same as theapparatus shown in FIG. 3 except that the apparatus shown in FIG. 8includes a strength increasing zone (aging zone) 230 where the (4)strength increasing step (aging step) is carried out right next to thechemical treatment zone 220 where the (3) chemical treatment step iscarried out. That is, after the (3) chemical treatment step, the (4)strength increasing step (aging step) is carried out in the strengthincreasing zone (aging zone) 230 to increase the peel strength of thesilicone porous body 20 relative to a resin film 10, thereby forming asilicone porous body 21 having a higher peel strength. The (4) strengthincreasing step (aging step) may be carried out by heating the siliconeporous body 20 in the same manner as described above using hot air fans(heating units) 231 disposed above and below the base 10, for example.The conditions including the heating temperature, the time, and the likeare not limited to particular values, and can be, for example, asdescribed above. After the (4) strength increasing step, similar to theprocess shown in FIG. 3, a laminated film in which the silicone porousbody 21 is formed on the base 10 is wound by a winding roller 251.

FIGS. 9 to 11 show another example of a continuous treatment process offorming a silicone porous body of the present invention. As shown in thecross sectional view of FIG. 9, this method includes, after the (3)chemical treatment step (for example, crosslinking treatment step) offorming a silicone porous body 20, (4) pressure-sensitiveadhesive/adhesive layer applying step (pressure-sensitiveadhesive/adhesive layer forming step) of coating the silicone porousbody 20 with pressure-sensitive adhesive/adhesive layer 30 and (5)intermediate layer forming step of causing the silicone porous body 20to react with the pressure-sensitive adhesive/adhesive layer 30 to forman intermediate layer 22. Except for these, the method shown in FIGS. 9to 11 is the same as the method shown in FIGS. 6 to 8. In, FIG. 9, the(5) intermediate layer forming step also serves as a step of increasingthe strength of the silicone porous body 20 (strength increasing step)so that the silicone porous body 20 changes to a silicone porous body 21having a higher strength after the (5) intermediate layer forming step.The present invention, however, is not limited thereto, and the siliconeporous body 20 may not change after the (5) intermediate layer formingstep, for example. The (4) pressure-sensitive adhesive/adhesive layerapplying step (pressure-sensitive adhesive/adhesive layer forming step)and the (5) intermediate layer forming step are not particularlylimited, and can be, for example, as described above.

FIG. 10 is a schematic view showing another example of a slot diecoating apparatus and another example of the method of forming asilicone porous body using the same. As can be seen, the coatingapparatus shown in FIG. 10 is the same as the apparatus shown in FIG. 7except that the apparatus shown in FIG. 10 includes a pressure-sensitiveadhesive/adhesive layer applying zone 130 a where the (4)pressure-sensitive adhesive/adhesive layer applying step is carried outright next to the chemical treatment zone 120 where the (3) chemicaltreatment step is carried out. In FIG. 10, the same heat treatment asthat carried out in the strength increasing zone (aging zone) 130 ofFIG. 7 can be carried out in an intermediate layer forming zone (agingzone) 130 disposed right next to the pressure-sensitiveadhesive/adhesive layer applying zone 130 a using hot air fans (heatingunits) 131 disposed above and below the base 10. That is, the apparatusshown in FIG. 10 carries out, after the (3) chemical treatment step, the(4) pressure-sensitive adhesive/adhesive layer applying step(pressure-sensitive adhesive/adhesive layer forming step) of applying apressure-sensitive adhesive or an adhesive to the silicone porous body20 to form a pressure-sensitive adhesive/adhesive layer 30 in thepressure-sensitive adhesive/adhesive layer applying zone 130 a usingpressure-sensitive adhesive/adhesive layer applying units 131 a. Insteadof applying the pressure-sensitive adhesive or the adhesive, forexample, an adhesive tape including the pressure-sensitiveadhesive/adhesive layer 30 may be adhered (taped) as described above.Thereafter, the (5) intermediate layer forming step (aging step) iscarried out in the intermediate layer forming zone (aging zone) 130 tocause the silicone porous body 20 to react with the pressure-sensitiveadhesive/adhesive layer 30, thereby forming an intermediate layer 22. Inthis step, the silicone porous body 20 changes to a silicone porous body21 having a higher strength as described above. The conditions of thehot air fans (heating units) 131 including the heating temperature, thetime, and the like are not limited to particular values, and can be, forexample, as described above.

FIG. 11 is a schematic view showing another example of a micro-gravurecoating apparatus and another example of the method of forming a porousstructure using the same. As can be seen, the coating apparatus shown inFIG. 11 is the same as the apparatus shown in FIG. 8 except that theapparatus shown in FIG. 11 includes a pressure-sensitiveadhesive/adhesive layer applying zone 230 a where the (4)pressure-sensitive adhesive/adhesive layer applying step is carried outright next to the chemical treatment zone 220 where the (3) chemicaltreatment step is carried out. In FIG. 11, the same heat treatment asthat carried out in the strength increasing zone (aging zone) 230 ofFIG. 8 can be carried out in an intermediate layer forming zone (agingzone) 230 disposed right next to the pressure-sensitiveadhesive/adhesive layer applying zone 230 a using hot air fans (heatingunits) 231 disposed above and below the base 10. That is, the apparatusshown in FIG. 11 carries out, after the (3) chemical treatment step, the(4) pressure-sensitive adhesive/adhesive layer applying step(pressure-sensitive adhesive/adhesive layer forming step) of applying apressure-sensitive adhesive or an adhesive to the silicone porous body20 to form a pressure-sensitive adhesive/adhesive layer 30 in thepressure-sensitive adhesive/adhesive layer applying zone 230 a usingpressure-sensitive adhesive/adhesive layer applying units 231 a. Insteadof applying the pressure-sensitive adhesive or the adhesive, forexample, an adhesive tape including the pressure-sensitiveadhesive/adhesive layer 30 may be adhered (taped) as described above.Thereafter, the (5) intermediate layer forming step (aging step) iscarried out in the intermediate layer forming zone (aging zone) 230 tocause the silicone porous body 20 to react with the pressure-sensitiveadhesive/adhesive layer 30, thereby forming an intermediate layer 22. Inthis step, the silicone porous body 20 changes to a silicone porous body21 having a higher strength as described above. The conditions of thehot air fans (heating units) 231 including the heating temperature, thetime, and the like are not limited to particular values, and can be, forexample, as described above.

[3. Application of Silicone Porous Body]

Since the silicone porous body of the present invention has a functionequivalent to an air layer as described above, it can be used for anobject including the air layer in place of the air layer, for example.The present invention is characterized in that it includes the siliconeporous body of the present invention, and other configurations are by nomeans limited.

Examples of the application of the present invention include heatinsulating materials, sound absorbing materials, dew condensationpreventing materials, and optical elements such as low refractive indexlayers, each of which includes the silicone porous body. These membersof the present invention can be used by disposing them at a place wherean air layer is needed, for example, if they are transparent. The formof these members is not limited to particular forms, and can be, forexample, a film.

The present invention can be also applied to, for example, aregenerative medical base including the silicone porous body. The basecan be, for example, scaffolding. The silicone porous body of thepresent invention has a porous structure which has a function equivalentto an air layer as described above. Since the void spaces of thesilicone porous body of the present invention are optimal to hold cells,nutrient sources, air, and the like, for example, the silicone porousbody of the present invention is useful as a regenerative medicalscaffolding, for example.

Examples of the member including the silicone porous body of the presentinvention include, besides these, total reflection members, ink imagereceiving materials, antireflection monolayers, moth eye monolayers, andpermittivity materials.

EXAMPLES

The examples of the present invention are described below. The presentinvention, however, is not limited by the following examples.

Example 1

In the present example, a porous structure of the present invention wasproduced as described below.

(1) Gelation of Silicon Compound

0.95 g of MTMS which is the precursor of a silicon compound wasdissolved in 2.2 g of DMSO. 0.5 g of 0.01 mol/L oxalic acid aqueoussolution was added to the mixture, and the resultant was stirred at roomtemperature for 30 minutes to hydrolyze MTMS, thereby preparingtris(hydroxy)methylsilane.

0.38 g of ammonia water having a concentration of 28% and 0.2 g of purewater were added to 5.5 g of DMSO, then the aforementioned mixture thathad been subjected to the hydrolysis treatment was added thereto, andthe resultant was stirred at room temperature for 15 minutes to gelatetris(hydroxy)methylsilane, thereby obtaining a gelled silicon compound.

(2) Aging Treatment

The aging treatment was carried out as follows. The mixture that hadbeen subjected to the gelation treatment was incubated at 40° C. for 20hours.

(3) Pulverizing Treatment

Subsequently, the gelled silicon compound that had been subjected to theaging treatment was granulated into pieces of several millimeters toseveral centimeters using a spatula. 40 g of IPA was added thereto, themixture was stirred lightly and then was allowed to stand still at roomtemperature for 6 hours, and a solvent and a catalyst in the gel weredecanted. This decantation treatment was repeated three times, and thesolvent replacement was completed. Then, the gelled silicon compound inthe mixture was subjected to high pressure medialess pulverization. Thispulverizing treatment was carried out using a homogenizer (product ofSMT Corporation, product name: UH-50) as follows. That is, 1.18 g of geland 1.14 g of IPA were added to 5 cc screw bottle and pulverized for 2minutes at 50 W and 20 kHz.

The gelled silicon compound in the mixture was pulverized by thepulverizing treatment, whereby the mixture was changed to a sol particleliquid of the pulverized product. The volume average particle sizeshowing particle size variations of the pulverized products contained inthe mixture measured by a dynamic light scattering nanotrac particlesize analyzer (product of NIKKISO CO., LTD., product name: UPA-EX150)was 0.50 to 0.70. 0.02 g of 0.3 wt % KOH aqueous solution, which is acatalyst, was added to 0.5 g of the sol particle liquid, therebypreparing a coating liquid.

(4) Formation of Coating Film and Formation of Silicone Porous Body

The coating liquid was applied to the surface of a base made ofpolyethylene terephthalate (PET) by bar coating, thereby forming acoating film. 6 μL of the sol particle liquid was applied to per squaremillimeter of the surface of the base. The coating film was treated at100° C. for one minute, and the crosslinking reaction among thepulverized products was completed. Thereby, a silicone porous bodyhaving a thickness of 1 μm in which the pulverized products arechemically bonded was formed on the base.

Comparative Example 1

A porous body was formed in the same manner as in Example 1 except thatKOH, which is a catalyst, was not added to the coating liquid.

(5) Measurement of Porous Structure Property

The porous body was peeled from the base, and the strength (abrasionresistance measured with BEMCOT®) was measured according to theaforementioned method. The refractive index, haze, and proportion ofvoid space were also measured.

The results are summarized in the following Table 1.

TABLE 1 Item Example 1 Comparative Example 1 Refractive index 1.16 1.12Haze 0.3 0.3 Porosity 59% 75% Abrasion resistance 78%  6%

As summarized in Table 1, the silicone porous body having a thickness of1 μm obtained in Example 1, despite its porous structure with highproportion of void space, has a sufficient strength and sufficientflexibility. This shows that the silicone porous body of the presentinvention obtained by a crosslinking reaction of aged silica compoundgel is very useful as a silanol porous body which achieves both the filmstrength and flexibility. Furthermore, the silicone porous body obtainedin Example 1 has favorable optical characteristics such as a lowrefractive index and a low haze. FIG. 4 shows the cross sectional SEMimage of the silicone porous body of Example 1. FIG. 5 shows the TEMimage of the microporous particles in the silicone porous body ofExample 1.

Example 2

In the present example, a porous structure of the present invention wasproduced as described below.

The “(1) gelation of silicon compound” and the “(2) aging treatment”were carried out in the same manner as in Example 1. Subsequently, the“(3) pulverizing treatment” was carried out in the same manner as inExample 1 except that an isopropyl alcohol (IPA) solution containing 1.5wt % photobase generation catalyst (product of Wako Pure ChemicalIndustries, Ltd., product name: WPBG 266) instead of 0.3 wt % KOHaqueous solution was added to the sol particle liquid, thereby preparinga coating liquid. The amount of the IPA solution containing thephotobase generation catalyst to be added relative to 0.75 g of the solparticle liquid was 0.031 g. Then, the “(4) formation of coating filmand formation of silicone porous body” were carried out in the samemanner as in Example 1. The porous body obtained in this manner afterdrying was irradiated with UV. The condition for the UV irradiation wasas follows. That is, the wavelength of the light was 360 nm and theamount of the light irradiation (energy) was 500 mJ. After UVirradiation, thermal aging at 60° C. was carried out for 22 hours,thereby forming a porous structure of the present example.

Example 3

A porous structure of the present example was produced in the samemanner as in Example 2 except that thermal aging was not performed afterUV irradiation.

Example 4

A porous structure of the present example was produced in the samemanner as in Example 2 except that, after the IPA solution containingthe photobase generation catalyst had been added, 0.018 g of 5 wt %bis(trimethoxy)silane was added to 0.75 g of sol liquid to adjust acoating liquid.

Example 5

A porous structure of the present example was produced in the samemanner as in Example 2 except that the amount of the IPA solutioncontaining the photobase generation catalyst to be added relative to0.75 g of the sol liquid was 0.054 g.

Example 6

After subjecting the porous body after drying to the UV irradiation inthe same manner as in Example 2 and before subjecting the porous body tothe thermal aging, the pressure-sensitive adhesive side of a PET film,to one side of which a pressure-sensitive adhesive (pressure-sensitiveadhesive/adhesive layer) is applied, was adhered to the porous body atroom temperature, and then the porous body was subjected to thermalaging at 60° C. for 22 hours. Except for this, a porous structure of thepresent example was produced in the same manner as in Example 2.

Example 7

A porous structure of the present example was produced in the samemanner as in Example 6 except that thermal aging was not carried outafter adhering the PET film.

Example 8

A porous structure of the present example was produced in the samemanner as in Example 6 except that, after the IPA solution containingthe photobase generation catalyst had been added, 0.018 g of 5 wt %bis(trimethoxy)silane was added to 0.75 g of the sol liquid to adjust acoating liquid.

Example 9

A porous structure of the present example was produced in the samemanner as in Example 6 except that the amount of the IPA solutioncontaining the photobase generation catalyst to be added relative to0.75 g of the sol liquid was 0.054 g.

The refractive index and haze of the porous structures of Examples 2 to9 were measured according to the aforementioned method. The results aresummarized in Tables 2 and 3.

TABLE 2 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Refractive index 1.14 1.15 1.15 1.16Haze 0.4 0.4 0.4 0.4 Porosity 65% 62% 62% 59% Abrasion resistance 70%70% 75% 78%

TABLE 3 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Refractive index 1.14 1.15 1.15 1.16Haze 0.4 0.4 0.4 0.4 Porosity 65% 62% 62% 59% Abrasion resistance 70%75% 75% 78%

As summarized in Tables 2 and 3, each of the silicone porous bodieshaving a thickness of 1 μm obtained in Examples 2 to 9 has favorableoptical characteristics such as a very low refractive index in the rangefrom 1.14 to 1.16 and a very low haze value of 0.4. Note that when thesilicone porous body has a very low refractive index, the siliconeporous body has a high proportion of void space. In fact, as summarizedin Tables 2 and 3, each of the silicone porous bodies has a highproportion of void space. Furthermore, each of the silicone porousbodies of Examples 2 to 9 has a sufficient strength and sufficientflexibility as in Example 1. Each of the coating liquids of Examples 2to 9 was visually observed after one week storage, and no change wasobserved. This shows that the coating liquid is superior in the storagestability and that a silicone porous body of stable quality can beproduced efficiently.

INDUSTRIAL APPLICABILITY

As described above, the silicone porous body of the present inventioncontaining the pulverized products of the gelled silicon compound formsa porous structure with void spaces, and the pulverized products arechemically bonded by the porous structure so that the porous structureis immobilized. Thus, the silicone porous body of the present invention,despite its structure with void spaces, can maintain a sufficientstrength and flexibility. The silicone porous body of the presentinvention is useful in that it can provide a void-provided structurewhich requires a film strength and flexibility. For example, thesilicone porous body of the present invention can be used, as a memberutilizing voids, for products in a wide range of fields, includingoptical elements such as low refractive index layers, heat insulatingmaterials, sound absorbing materials, and ink image receiving members.

EXPLANATION OF REFERENCE NUMERALS

-   10 base-   20 porous structure-   20′ coating film (precursor layer)-   20″ sol particle liquid-   21 porous structure (porous body) with improved strength-   101 delivery roller-   102 coating roller-   110 oven zone-   111 hot air fan (heating unit)-   120 chemical treatment zone-   121 lamp (light irradiation unit) or hot air fan (heating unit)-   130 a pressure-sensitive adhesive/adhesive layer applying zone-   130 intermediate forming zone-   131 a pressure-sensitive adhesive/adhesive layer applying unit-   131 hot air fan (heating unit)-   105 winding roller-   106 roller-   201 delivery roller-   202 liquid reservoir-   203 doctor (doctor knife)′-   204 micro-gravure-   210 oven zone-   211 heating unit-   220 chemical treatment zone-   221 lamp (light irradiation unit) or hot air fan (heating unit)-   230 a pressure-sensitive adhesive/adhesive layer applying zone-   230 intermediate forming zone-   231 a pressure-sensitive adhesive/adhesive layer applying unit-   231 hot air fan (heating unit)-   251 winding roller

1. A method of producing a silicone porous body, comprising steps of:preparing a liquid containing silicon compound microporous particles;adding a catalyst for chemically bonding the silicon compoundmicroporous particles to the liquid; and chemically bonding themicroporous particles by catalysis.
 2. The method according to claim 1,wherein the catalysis in the bonding step is wet-type treatment and/ordry-type treatment.
 3. The method according to claim 1, wherein thesilicon compound microporous particle includes a silica sol fineparticle.
 4. The method according to claim 3, wherein the silica solfine particle is obtained by pulverizing a gelled silica compound. 5.The method according to claim 4, wherein the pulverization is performedby high pressure medialess pulverizing.
 6. The method according to anyone of claim 1, wherein in the bonding step, the chemical bond is acrosslinking bond.
 7. The method according to any one of claim 1,wherein a drying temperature for the catalysis in the bonding step is50° C. or more and less than 200° C.
 8. The method according to any oneof claim 1, further comprising a step of: adding a crosslinkingassisting agent for indirectly bonding the silicon compound microporousparticles to the liquid.
 9. The method according to claim 8, wherein anamount of the crosslinking assisting agent to be added relative to aweight of the silicon compound microporous particle is in a range from0.01 wt % to 20 wt %.